Europe, UK, Asia & RoW: [email protected] +44 (0)1622 859444 | USA & Canada: [email protected] +1 401-583-7846

What is an Infrared-Cut Filter, and How to Choose the Right One for your Application?

27th Nov 2018

Camera detector systems such as ANPR, CMOS and CCD do a fantastic job of recording accurate colour images in daylight. The trouble is that the camera sensors also detect near-infrared light way beyond what the human eye is capable of. This is important for night vision recording but, in daylight hours, the infrared light distorts the colours of recorded images. The solution is an IR-cut filter.

Day-night cameras make good use of IR-cut filters. They work by filtering out unwanted IR light to prevent it distorting daylight image colours, presenting them as much more true to life. When the camera is operating in night mode, the IR-cut filter cuts out to allow the light sensitivity of the camera to reach down to very low lux levels.

What to consider when choosing an infrared-cut filter for your camera system?

Accuracy and control are of paramount importance when it comes to building a camera of quality that can be relied upon to deliver the very best recorded images with minimal colour distortion. Both can be improved with the use of an IR-cut filter that allows the sharpest possible transitions between the transmitting and reflecting bands. So what makes an IR-cut filter stand out from the rest? How to choose the right infrared-cut filter for precision applications where there is absolutely no room for error or inaccuracy?

Coating choice

The answer lies in the coating and the quality of the substrate. Our research and analysis have shown that an anti-reflective hot mirror coating on a quality borosilicate substrate offers the optimum solution. The coating is applied to the rear surface, greatly improving the light transmission.

Substrate choice

Borosilicate as a substrate presents excellent chemical resistance to saline and acidic solutions. It does not degrade under normal conditions and, thanks to its low thermal expansion, the optical component it is used within is able to survive rapid changes in temperature whilst at the same time maintaining structural integrity. Borosilicate really does stack up in comparison to other materials that are prone to cracking or shattering in extreme climatic conditions.

How to resolve HD blotching

For HD cameras where blotching can be a highly undesirable effect, the addition of a scratch-dig filter on a pre-polished substrate will resolve the issue.

Infrared-Cut Filters from Knight Optical

Knight Optical has the technical expertise to craft precision, custom-made IR-cut filters in any size, shape or thickness with a range of transmission wavelengths to suit individual requirements. For further information and technical specifications visit